Reinforced sealing technique for an integrated-circuit package

ABSTRACT

One or more reinforcement pins are inserted between the lid and base of a sealed integrated-circuit package. The reinforcement pins reinforce a sealing layer between the lid and the base, particularly against shear forces exerted on the sealing layer between the lid and the base of a package. Shorter pins are provided which do not extend through the lid or base. Longer pins are provided which extend through the lid or base, with the ends of the pins being mechanically secured to the lid or base and sealed with solder, glass, or epoxy material.

This is a division of application Ser. No. 07/951,078 filed Sep. 25,1992, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to packaging techniques for integrated circuitsand, more particularly, to techniques for scaling an integrated-circuitpackage.

2. Prior Art

A hermetically-sealed package, or package assembly for an integratedcircuit typically includes a base in which is formed a cavity for theintegrated-circuit die. The base of the package is formed of a ceramicor a metallic material. A lid of ceramic or metallic material is sealedto the base with an appropriate layer of sealing material, such asglass, solder, or epoxy. Sometimes an intermediate, thin sealing ring ispositioned between the base and the lid so that two layers of sealingmaterial are used, one on each side of the sealing ring. Currently, allof the sealing techniques used in packaging of integrated circuits relyupon the adhesion strength of the layer of sealing material. Because ofthe differences in the temperature coefficients of expansion (TCE) ofthe various materials used in a package, the adhesion of the sealingmaterial fails and the lids of the packages peel away frown their bases.This occurs particularly when a package is subjected to pressure-pottesting or to thermal-cycle testing, where the shear forces cause thesealing materials to fail at the margins between the sealing materialsand the package elements.

With variations in temperature, the various components of a package, aswell as the sealing layers, expand or contract at different rates sothat shear forces are generated at the interfaces between the differentelements and the sealing materials. The shear strengths of the sealingmaterials, such as glass, solder, or epoxy are relatively weak so thatfailures occur at the margin of the sealing material near the packageelements. Typically, an epoxy material fails with a shear pressure of 1to 5 kpsi. The materials of the package elements such as the base or lidare much stronger under shear loads. For example a metal has a failureshear strength of 10-30 kpsi.

One solution to the problem of lids peeling from packages is to attemptto match the TCE's of the various materials of the package assembly.This is difficult to accomplish and has the disadvantage that moreexpensive materials often must be used.

The need has arisen for an improved integrated-circuit packagingtechnique which enhances and reinforces currently-used packagingtechnique by increasing the adhesion strength of adhesive or bondingmaterial between the lid and the base of an integrated-circuit package.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide an improvedpackaging technique for integrated circuits, which techniques increasesthe performance of the adhesion or bonding layer between the lid and thebase of an integrated-circuit package.

In accordance with this and other objects of the invention, theinvention provides for inserting one or more reinforcement pins betweenthe lid and base of an integrated-circuit package. This invention isapplicable to a number of different package types, such aspin-grid-array (PGA), side-brazed, and epoxy-sealed packages of varioustypes. The reinforcement pins are used to reinforce a sealing layerbetween the lid and the base, particularly when shear forces are exertedon the boundaries between the sealing layer and the lid or base of thepackage. The length of the reinforcement pins is optional. Shorter pinsdo not extend through the lid or base. Longer pins can extend throughthe lid or base and their ends are mechanically secured to the lid orbase and sealed with solder, glass, or epoxy material.

The invention provides a package structure and a method of packaging anintegrated circuit. An integrated-circuit die is mounted within a cavityformed in a base of a package. A lid is positioned over theintegrated-circuit die and the base and lid are sealed with a sealinglayer positioned between the base and the lid.

The invention contemplates using at least one reinforcement pin, whichextends through the sealing layer and at least partially through thebase and at least partially through the lid. The reinforcement pinprovides reinforcement for the sealing layer between the base and thelid so that the package can resist shear forces tending to rupture thesealing layer between the lid and the base of the package. The inventionis useful with packages which use an intermediate sealing ring betweenthe lid and the base. The reinforcement pin extends through this type ofring and through sealing layers formed adjacent to the top and bottomsurfaces of this ring.

A pin extends at least partially through an undersize aperture in thebase and at least partially through an undersize aperture in the lid tosecure the reinforcement pin to the base and the lid. The pin can extendthrough either or both of the lid and the base of a package. Theextending end or ends of a reinforcement pin are fixed to a lid or base,for example by being stamped, pressed, or punched and sealed with anumber of materials, such as solder, glass, or epoxy.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthis specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention:

FIG. 1 is a partial sectional view of a prior art epoxy sealed package.

FIG. 2 is a partial sectional view of a prior art side-brazed package,which uses an intermediate sealing ring between the lid and the body ofthe package.

FIG. 3 is a sectional view of a prior art package using a ring, which ispositioned between the lid and the body of the package.

FIG. 4 is a partial sectional view of a package configuration using areinforcement pin to increase the mechanical strength of the seal for anintegrated-circuit package in accordance with the present invention.

FIG. 5 is a partial sectional view of a portion of a packageconfiguration which uses a reinforcement pin which extends through lidand the base of a package, where the ends of the pin are sealed with asealing material in accordance with the present invention.

FIG. 6 is a top view of a pin-grid-array PGA) package configuration, inwhich a number of reinforcement pins secure a lid to a base of a packagein accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. While the invention will be described in conjunction with thepreferred embodiments, it will be understood that they are not intendedto limit the invention to these embodiments. On the contrary, theinvention is intended to cover alternatives, modifications andequivalents, which may be included within the spirit and scope of theinvention as defined by the appended claims.

FIG. 1 shows a prior art epoxy-sealed package assembly 10, such as aquad flat pack package. A base 12 has a cavity 14 formed therein forcontaining an integrated-circuit die 16. The integrated-circuit die 16is attached to an interior surface 18 of the base 12 using a suitablelayer 19 of bonding material, such as silver-filled epoxy material. Thebase 12 is formed of a metal, FR4, a pre-molded material, or a ceramicmaterial, such as alumina Al₂ O₃. A number of metal leads (typicallyshown as 20) have an inner portion 22 which extends into the cavity 14.Respective bonding wires (typically shown as 24) have one endwire-bonded to respective bonding pads on the top surface of theintegrated-circuit die 16. The other end of the respective bonding wiresare bonded to the ends of respective metal leads, as indicated in theFigure. A lid 26, formed of gold-plated kovar, aluminum, ceramicmaterial, FR4, or premolded material overlies the cavity 14. The innerportion 22 of a metal lead 20 extends into the cavity 14 through anepoxy seal 28. The epoxy seal 28 serves as a bonding material betweenthe base 12 and the lid 26.

Similarly, for some ceramic packages, the sealing material could be asoft glass. The soft glass seal 28 is, in general, made oflead-zinc-borate material and is sealed at 400-450 degrees Centigrade.The lead-zinc-borate material has a TCE of 8-10 ppm/deg. C. Incomparison, ceramic material has a TCE of 5-6 ppm/°C. This mismatch inTCE's is a source of stress in the bonding material, particularly afterthe package is assembled and is cooled to an ambient operatingtemperature of 24 degrees C. The bond layer may also have intermetalliclayers formed in it due to metal migrating into the glass material. Theseal has a mechanical strength of 7-8000 psi. The area stressed iscontained within the horizontal and vertical cross-section of the sealarea.

FIG. 2 shows a sectional view of a prior art side-brazed package 100. Abase 102 has a cavity 104 formed therein for containing anintegrated-circuit die 106 which is attached to an interior surface 108of the base 102 using a suitable layer 110 of bonding material, such asgold-silicon eutectic or silver glass. The base is generally formed of aceramic material, such as alumina Al₂ O₃. A number of metal traces(typically shown as 112) are deposited on the exterior shoulders of thebase 102 adjacent to the cavity 104. These metals traces are formed ofmolybdenum/tungsten material. Bonding wires (typically shown as 114)have one end wire-bonded to respective bonding pads on the top surfaceof the integrated-circuit die 106. The other end of the respectivebonding wires are bonded to the ends of respective metal leads, asindicated in the Figure. A lid 116, formed of gold-plated kovar orceramic material, overlies the cavity 104. A ceramic seal ring 118extends around the base 102 of the package. A soft glass or solder seal120 is formed between the top surface 122 of the ceramic seal ring 118and a lower surface 124 of the lid 116.

A metal lead 130 formed of kovar/A42 is brazed or soldered to the sideof the base 102 using a layer 132 of material formed of eutectic gold ora tin/lead alloy 80/20 material. Brazed solder seals having TCE mismatchproblems and inter metallic formations are common. The TCE of tin is 23ppm/deg. C.; Molybdenum is 4.8 ppm/deg. C.; alumina is 5-6 ppm/deg. C.;and gold is 14 ppm/deg. C. A nickel-alloyed, gold-plated is used forgood solder or brazing wettability. Very often too much gold is formedand dissolved during the brazing or soldering process, producing poormechanical strength in the bond. A solder seal is less preferred becauseof the embrittlement caused by the inter metallic bond, which has halfas much strength as a brazed seal. Indium and silver are added to solderseals to match TCE's, reduce shrinkage voids, and increase mechanicalstrength for fatigue resistance.

FIG. 3 illustrates a package assembly 200, which uses a prior art ring202 intermediate a lid 204 and a body 206, which are assembled at hightemperature and cooled to ambient temperature. The lid 204 and body 206are usually formed of different materials. The lid can be formed ofmetal, ceramic, or printed circuit board (PCB) material. The body can beformed of metal, plastic, PCB, or premolded material. The TCE mismatchcauses shrinkage of the different material at different rates. Thisproduces mechanical stress at the bonding layer. These bonds will failif these stresses are beyond maximum tolerable limits.

FIG. 4 shows a portion of an integrated-circuit package configuration250, according to the invention. This package configuration uses areinforcement pin 252 to increase the mechanical strength of the sealfor the integrated-circuit package 250. The package includes a base 254which has a top sealing surface 256 formed around its margins. A lid 260has a lower sealing surface 262 around its margins. A layer of sealingmaterial 264 is formed between the top sealing surface 256 of the base254 and the lower sealing surface 262 of the lid 260.

The reinforcement pin 252 serves as a mechanical means for mechanicallyholding the base 254 and the lid 260 together and provides additional,mechanical sealing between the base and the lid. The reinforcement pin252 is formed of a metal, such as, for example, gold-plated kovar. Thepin 252 extends through the sealing layer 264 and at least partiallyinto the base 254 and at least partially into the lid 260. One end 272of the reinforcement pin extends through a somewhat undersized aperture274 formed in the base 254. The other end 276 of the reinforcement pin252 extends through a somewhat undersized aperture 278 formed in the lid260. A number of reinforcement pins can be pressed into the base and thelid and are used to provide mechanical reinforcement for the layer ofsealing material 264.

The undersized apertures 274, 278 are formed in the base and lidelements of the package using conventional techniques, such as used forthe apertures for the leads of a pin-grid-array PGA package forintegrated circuit. The internal surfaces of the undersized apertures274, 278 are coated with a thin layer of material such as tin, gold, ornickel. When reinforcement pins are inserted in the slightly undersizeapertures and the assembly is subsequently heated, the reinforcementpins are securely fixed in place. A partial assembly of a lid with somereinforcement pins can be prepared prior to attachment of anintegrated-circuit die to a base.

The reinforcement pins have much greater shear strength than a layer ofsolder or epoxy material. The reinforcement pins therefore serve toprevent catastrophic failure of the weaker package sealing layer duringoperating conditions such as are tested by pressure pot or temperaturecycling tests, where the sealing layer is likely to fail in a shearmode. The reinforcement pins pull the lid and the base together andprovide additional sealing of the package.

FIG. 5 shows another embodiment of the invention which uses a longerreinforcement pin 300. One end 302 of the pin 300 extends completelythrough an aperture 304 formed through a lid member 306. The other end308 of the pin 300 extends completely through an aperture 310 formedthrough a base member 312. The intermediate portion 314 of the pin 300extends through a sealing ring 316. The top surface 318 of the sealingring 316 is sealed to the underside 320 of the lid member 306 with asealing layer 322. The lower surface 324 of the sealing ring 316 issealed to the upper surface 326 of a metal layer 326 formed on the topsurface of the base member 312, as indicated in the Figure.

The pin 300 can be press-fit and its ends stamped, punched, or rolledover with a press. The tip 330 of the one end 302 of the pin 300 isshown rolled over, as indicated in FIG. 5. A gold-plated, metallized pad332 is provided on the top, outside surface 334 of the lid member 306.The tip 330 of the pin 300 is sealed to the lid member 306 with a blob336 of sealing material. If the blob 336 is solder, the metallized pad332 provides a surface for the solder. Alternatively, the blob ofsealing material can be formed of glass or epoxy material.

The base member 312 of the package is optionally formed of a number ofmaterials, depending on the package type. Material for the base include,for example, metal, ceramic, and circuit board materials, such as epoxyglass or FR4 material.

The other tip 340 at the other end 308 of the pin 300 is also rolledover, as indicated in the Figure. A gold-plated, metallized pad 342 isalso provided, as required, on the bottom surface of the base member312. The other tip 340 of the pin 300 is sealed to the base member 312with a blob 344 of sealing material. If the blob 344 is solder, themetallized pad 342 provides a wettable surface for the solder.Alternatively, the blob of sealing material can be formed of glass orepoxy material.

FIG. 6 shows in reduced scale a top view of a pin-grid-array PGA packageconfiguration 350, in which a number of reinforcement pins 352 secure alid 354 to a base 356.

The foregoing descriptions of specific embodiments of the presentinvention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteaching. The embodiments were chosen and described in order to bestexplain the principles of the invention and its practical application,to thereby enable others skilled in the art to best utilize theinvention and various embodiments with various modifications as aresuited to the particular us contemplated. It is intended that the scopeof the invention be defined by the Claims appended hereto and theirequivalents.

We claim:
 1. A package for an integrated-circuit die, comprising:a basehaving a top sealing surface thereon, said base having anintegrated-circuit die fixed thereto; a lid having a lower sealingsurface thereon, said lid disposed overlying said base such that saidlower sealing surface of said lid is disposed proximate to said topsealing surface of said base and such that said integrated-circuit dieis disposed between said lid and said base; a first sealing layerlocated between said top sealing surface of said base and said lowersealing surface of said lid; and mechanical means for reinforcing saidsealing layer against shear forces occurring between said base and saidlid and for mechanically and permanently holding said base and said lidtogether to provide reinforcement against shear forces and to provideadditional sealing between said base and said lid, wherein saidmechanical means includes a pin disposed extending from at leastpartially within said base, through said top sealing surface of saidbase, through said first sealing layer, through said lower sealingsurface of said lid, and at least partially into said lid.
 2. Thepackage of claim 1 wherein said mechanical means includes a pinextending through said first sealing layer and at least partiallythrough an undersized aperture disposed in said base and at leastpartially through an undersized aperture disposed in said lid.
 3. Thepackage of claim 1 wherein said mechanical means for mechanicallyholding said base and said lid tightly together includes a pin extendingthrough said first sealing layer and through said lid to provide a firstexposed end of said pin.
 4. The package of claim 3 including means forfixing said first exposed end of said pin to said base.
 5. The packageof claim 4 wherein said means for fixing said first exposed end of saidpin to said base includes solder.
 6. The package of claim 4 wherein saidmeans for fixing said first exposed end of said pin to said baseincludes glass.
 7. The package of claim 4 wherein said means for fixingsaid first exposed end of said pin to said base includes epoxy.
 8. Thepackage of claim 1 wherein said mechanical means for mechanicallyholding said base and said lid tightly together includes a pin extendingthrough said first sealing layer and through said base to provide anexposed end of said pin.
 9. The package of claim 8 including means forfixing said second exposed end of said pin to said lid.
 10. The packageof claim 9 wherein said means for fixing said second exposed end of saidpin to said lid includes solder material.
 11. The package of claim 9wherein said means for fixing said second exposed end of said pin tosaid lid includes glass material.
 12. The package of claim 9 whereinsaid means for fixing said second exposed end of said pin to said lidincludes epoxy material.
 13. The package of claim 1 further includingsaid mechanical means for mechanically holding said base and said lidtogether to provide additional sealing between said base and said lidincludes a plurality of pins extending through said first sealing layerand at least partially into said base and at least partially into saidlid.
 14. The package of claim 1 wherein said base has a cavity formedtherein for receiving said integrated-circuit die.
 15. The package ofclaim 1 further comprising:a sealing ring, positioned adjacent to saidbase, said sealing ring having a top sealing surface and a bottomsealing surface, said sealing ring disposed between said top sealingsurface of said base and said lower sealing surface lid; a secondsealing layer located between said top sealing surface of said base andsaid bottom sealing surface of said sealing ring; said first sealinglayer located between said lower sealing surface of said lid and saidtop sealing surface of said sealing ring; and mechanical means formechanically holding said base, said sealing ring, and said lid tightlytogether including a pin extending through an aperture formed throughsaid sealing ring, said pin extending from at least partially withinsaid base, through said second sealing layer, through said sealing ring,through said first sealing layer, and at least partially into said lid.16. A package for an integrated-circuit die, comprising:a base having atop sealing surface thereon said base having an integrated-circuit diefixed thereto; a lid having a lower sealing surface thereon, said liddisposed overlying said base such that said lower sealing surface ofsaid lid is disposed proximate to said top sealing surface of said baseand such that said integrated-circuit die is disposed between said lidand said base; a first sealing layer located between said top sealingsurface of said base and said lower sealing surface of said lid; and apin disposed extending from at least partially within said base, throughsaid top sealing surface of said base, through said first sealing layer,through said lower sealing surface of said lid, and at least partiallyinto said lid, wherein said pin provides reinforcement for said sealinglayer against shear forces occurring between said base and said lid andfor mechanically and permanently holding said base and said lidtogether.
 17. The package of claim 16 wherein said pin extends throughsaid first sealing layer and at least partially through an undersizedaperture disposed in said base and at least partially through anundersized aperture disposed in said lid.
 18. The package of claim 16wherein said pin extends through said first sealing layer and throughsaid lid such that a first end of said pin is exposed.
 19. The packageof claim 18 including means for fixing said first exposed end of saidpin to said lid.
 20. The package of claim 19 wherein said means forfixing said first exposed end of said pin to said lid includes solder.21. The package of claim 19 wherein said means for fixing said firstexposed end of said pin to said lid includes glass.
 22. The package ofclaim 19 wherein said means for fixing said first exposed end of saidpin to said lid includes epoxy.
 23. The package of claim 16 wherein saidpin extends through said first sealing layer and through said base toprovide an exposed end of said pin.
 24. The package of claim 23including means for fixing said second exposed end of said pin to saidbase.
 25. The package of claim 24 wherein said means for fixing saidsecond exposed end of said pin to said lid includes solder material. 26.The package of claim 24 wherein said means for fixing said secondexposed end of said pin to said lid includes glass material.
 27. Thepackage of claim 24 wherein said means for fixing said second exposedend of said pin to said lid includes epoxy material.
 28. The package ofclaim 16 further including wherein a plurality of pins extend throughsaid first sealing layer and at least partially into said base and atleast partially into said lid.
 29. The package of claim 16 wherein saidbase has a cavity formed therein for receiving said integrated-circuitdie.
 30. The package of claim 16 further comprising:a sealing ring saidsealing ring having a top sealing surface and a bottom sealing surface,said sealing ring disposed between said top sealing surface of said baseand said lower sealing surface of said lid; a second sealing layerformed between said top sealing surface of said base and said bottomsealing surface of said sealing ring; said first sealing layer locatedbetween said lower sealing surface of said lid and said top sealingsurface of said sealing ring; and mechanical means for mechanicallyholding said base, said sealing ring, and said lid tightly togetherincluding said pin extending through an aperture formed through saidsealing ring, said pin extending from at least partially within saidbase, through said second sealing layer, through said sealing ring,through said first sealing layer, and at least partially into said lid,wherein said pin provides mechanical reinforcement for said sealinglayer against shear forces occurring between said base, said lid, andsaid sealing ring and for mechanically and permanently holding saidbase, said sealing ring, and said lid together and to provide additionalsealing between said base, said sealing ring, and said lid.
 31. Apackage for an integrated-circuit die, comprising:a base having a topsealing surface thereon, said base having an integrated-circuit diefixed thereto; a lid having a lower sealing surface thereon, said liddisposed overlying said base such that said lower sealing surface ofsaid lid is disposed proximate to said top sealing surface of said baseand such that said integrated-circuit die is disposed between said lidand said base; a sealing ring, positioned adjacent to said margins ofsaid base, said sealing ring having a top sealing surface and a bottomsealing surface, said sealing ring disposed between said top sealingsurface of said base and said lower sealing surface of said lid; a firstsealing layer formed between said top sealing surface of said base andsaid bottom sealing surface of said sealing ring; a second sealing layerformed between said lower sealing surface of said lid and said topsealing surface of said sealing ring; and a pin disposed extendingthrough an aperture formed through said sealing ring, said pin extendingfrom at least partially within said base, through said first sealinglayer, through said sealing ring, through said second sealing layer, andat least partially into said lid, wherein said pin provides mechanicalreinforcement for said sealing layer against shear forces occurringbetween said base, said lid, and said sealing ring and for mechanicallyand permanently holding said base, said sealing ring, and said lidtogether and to provide additional sealing between said base, saidsealing ring, and said lid.
 32. The package of claim 31 wherein said pinextends through said first sealing layer and at least partially throughan undersized aperture disposed in said base and at least partiallythrough an undersized aperture disposed in said lid.
 33. The package ofclaim 31 wherein said pin extends through said lid such that a first endof said pin is exposed.
 34. The package of claim 33 including means forfixing said first exposed end of said pin to said lid.
 35. The packageof claim 34 wherein said means for fixing said first exposed end of saidpin to said lid includes solder.
 36. The package of claim 34 whereinsaid means for fixing said first exposed end of said pin to said lidincludes glass.
 37. The package of claim 34 wherein said means forfixing said first exposed end of said pin to said lid includes epoxy.38. The package of claim 31 wherein said pin extends through said baseto provide a second exposed end of said pin.
 39. The package of claim 38including means for fixing said second exposed end of said pin to saidbase.
 40. The package of claim 39 wherein said means for fixing saidsecond exposed end of said pin to said lid includes solder material. 41.The package of claim 39 wherein said means for fixing said secondexposed end of said pin to said lid includes glass material.
 42. Thepackage of claim 39 wherein said means for fixing said second exposedend of said pin to said lid includes epoxy material.
 43. The package ofclaim 31 further including a plurality of pins extend through saidsealing ring, said first and second sealing layers, and at leastpartially into said base and at least partially into said lid.
 44. Thepackage of claim 31 wherein said base has a cavity formed therein forreceiving said integrated-circuit die.